Boiling water reactors typically include a coolant recirculation system providing forced convection flow through the core. A portion of the water flowing through the downcomer annulus is withdrawn from the reactor vessel via a recirculation water outlet and is fed under pressure into a plurality of jet pump assemblies distributed about the core shroud within the downcomer annulus. The jet pump assemblies produce a forced convection flow through the core, providing the required reactor core water flow.
The riser pipe of a jet pump assembly is supported and stabilized within the reactor vessel by a riser brace attached to the riser pipe and to an attachment wall, the attachment wall typically being the reactor vessel wall. The riser brace provides lateral and radial support to the riser pipe. In addition, the riser brace is designed to accommodate the differential thermal expansion resulting from reactor start-up and heat-up, and to accommodate the flow-induced vibration incumbent in the reactor water circulation system due to reactor recirculation pumps.
Commonly, the riser brace is attached to the riser pipe and to the attachment wall by being welded to the riser pipe and to the attachment wall. The riser brace is normally attached to the riser pipe via a weld. However, cracks have been known to develop in these welds. Also, intergranular stress corrosion cracking (IGSCC) resulting from corrosion, radiation, and/or stress occurs in the welds between the riser brace and the riser pipe. Cracks can grow in size and reach critical sizes for mechanical fatigue crack to the detriment of the jet pump assembly.
Accordingly, there is a need for reinforcing the weld between a riser pipe and a riser brace of a jet pump assembly, including mitigating or repairing a cracked weld to maintain structural integrity of the jet pump assembly and to avoid excessive vibration of the riser pipe or brace. There is an additional need for redundant structural support to the weld between a riser pipe and riser brace. Previously proposed designs are complicated, requiring the inlet mixer to be removed. Previous designs must also be extremely accurate to fit correctly and must be machined in the field for each particular application.